1. Field of the Invention
The invention relates to aqueous dispersions containing organopolysiloxane/polyurea copolymers and a process for the preparation thereof.
2. Background Art
Aqueous polyurethane/polyurea dispersions and processes for their preparation are known. In this context, reference may be made, for example, to DE 11 84 946 B, DE 11 78 586 B, DE 14 95 745 C3, DE 20 19 324 C3 and DE 28 07 861 A1. The dispersions described therein are prepared based on the principle of incorporating hydrophilic centers into a macromolecular chain of a polyurethane/polyurea molecule. These hydrophilic centers, or internal emulsifiers as they are referred to, are ionic groups or ether groups in these dispersions. The ionic groups are either incorporated into the prepolymer in the form of specially functionalized diols or are used in the form of modified amines for chain extension of the prepolymers, which each have at least two terminal NCO groups.
Dispersions which are prepared using organic solvents during polyaddition have the disadvantage that the organic solvent has to be distilled off and recycled by a relatively complicated procedure. Solvent-free processes for the preparation of polyurethane dispersions are also known, for example the so-called melt dispersing process disclosed in DE 17 70 068 C3, in which an oligourethane modified with ionic groups is used. This process is suitable in particular for the preparation of cationically modified polyurethanes or for the preparation of anionic polyurethanes containing carboxylate groups. The required combination of process steps, e.g. isocyanate polyaddition and chain extension constitute a considerable disadvantage to such synthetic methods.
Employing prepolymers containing both sulfonate and NCO groups, polyaddition reactions involving the NCO groups with difunctional compounds reactive with NCO groups may be carried out while dispersing the reactants in a dispersing medium. In this context, reference may be made, for example, to DE 2 446 440 C3. A disadvantage of this process is that only polymers containing sulfonate groups may be obtained.
DE 199 58 525 A1 discloses dispersions which are obtained from silyl-functional polymers. A disadvantage is that the special polymers have to be synthesized in a separate step. Polyurethane dispersions having disiloxane groups are disclosed in DE 44 13 562 A1. Here too, a special synthesis of prepolymers is required, and in addition, the siloxane content is extremely low. The preparation of polyureas by interfacial polyaddition according to DE 19 46 942 A, starting from monomeric diisocyanates and diamines in aqueous solution, is known. However, the use of siloxane-containing polymers in this process is not suggested.
Organopolysiloxane/polyurea block copolymers are known and are prepared from aminoalkyl-terminated siloxanes and diisocyanates. In this context, reference may be made, for example, to Polymer, Vol. 25 (1984), page 1800 et seq. Advantageous properties of these products are an obtainable high siloxane content (>90%) and their thermoplasticity. A disadvantage is that they are once again readily dispersible only by the incorporation of ionic, polar, or hydrophilic groups, e.g. polyethers, so that properties of the underivatized organopolysiloxane/polyurea block copolymers are largely lost.